224 PARASITES OF GIPSY AND BROWN-TAIL MOTHS. 



It is yet too soon to begin to speculate upon what the actual out- 

 come in specific instances will be. An investigation of the parasites 

 of the fall web worm was undertaken in the fall of 1910 on the suppo- 

 sition that Compsilura would find it an acceptable host, but although 

 it is freely attacked when outside of its web in rearing cages in the 

 laboratory, it was not at all commonly attacked in the open, as will 

 be seen by reference to the brief summary of the results of the work 

 in the concluding pages of this bulletin. 



There has never been a good opportunity to study the parasites 

 of the Tachinidse, owing to the fact that some of the species pupate 

 upon or beneath the surface of the soil, and are therefore difficult to 

 find in sufficient quantities to make a comprehensive study possible. 

 So abundant was Compsilura, however, as to make it possible to 

 collect its puparia in considerable abundance and with comparatively 

 little trouble at the base of trees upon which the gipsy-moth cater- 

 pillars were common, and accordingly a number was so collected in 

 the late summer of 1910. Not enough attention was given to the 

 work to make the results as definite as is desired, but these were 

 sufficient to indicate that secondary parasitism was undoubtedly of 

 very common occurrence, and that it might be a factor of some con- 

 sequence in limiting the effectiveness of the parasite. No less than 

 six species of secondaries were reared, including Monodontomerus 

 sereus, which was common, Dibrachys, another small chalcidid, a 

 species of Chalcis, a proctotrypid, and a Phygadeuon. It is hoped 

 that circumstances will permit of a more thorough study of this 

 subject in 1911, and should the parasite show an increase propor- 

 tionate to that which was indicated by its abundance in 1910 over 

 that of 1909, the project should be very easy of accomplishment. 



It is fortunate that, under the present circumstances, with the 

 gipsy moth and the brown-tail moth both exceedingly abundant and 

 uncontrolled, there should be at least one parasite which was equally 

 drawn toward both. It is easily possible that the first individuals 

 which are reared upon the brown-tail moth as a host may attack the 

 full-fed caterpillars for a partial second generation the same season, 

 and then, together with the bulk of the brood coming from this host, 

 turn their undivided attention to the gipsy-moth caterpillars. In a 

 similar manner the first individuals to go through their transforma- 

 tions upon the gipsy moth, together with the partial second genera- 

 tion upon the brown-tail moth, may attack the less advanced gipsy- 

 moth caterpillars for a partial third brood before the necessity for 

 an alternate host becomes apparent. 



There is thus possible uninterrupted increase for two complete gen- 

 erations at least, and probably for a partial third, but unfortunately 

 the necessity for an alternate host, though delayed until no more than 

 one such host is necessary in order that the seasonal cycle may be 



